After injection of the local anaesthetic, the sciatic nerve is more easily visualised due to the contrast between the bright (hyperechoic) sciatic nerve and the background of the black (anechoic) local anaesthetic
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The visibility of the sciatic nerve and its branches are often reduced in the very obese patients
In obese patients it may be required to use a curved array transducer in order to perform a popliteal sciatic nerve block
However, the sciatic branches – the tibial nerve and the common peroneal nerve – are often sonographically visible near the popliteal crease, where they are usually superficially located. Even in obese patients
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The endpoint of ultrasound guided peripheral nerve blockade is complete perineural spread of local anaesthetic
This can be obtained by repositioing the tip of the needle during injection
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The in-plane approach to block the two branches of the sciatic nerve – the tibial nerve and the peroneal nerve – allows real-time visualisation of the needle tip, the target nerves and the perineural spread of the local anesthetic
It also gives the opportunity to relocate the needle tip, if the spread is not perfect
The real time ultrasound imaging also makes it possible to avoid piercing the peroneal nerve, when the needle is advanced towards the tibial nerve
It is important not to penetrate the target nerves with the block needle and especially not to inject local anaesthetic intraneurally
Insert the needle tangentially to the branches of the sciatic nerve in the popliteal fossa
Needle is indicated by arrow head
You can touch the nerve with the needle, but you should not pierce it
And especially you should not inject local anaesthetic intraneurally
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It is also possible to move the probe proximal to the bifurcation of the sciatic nerve and block the nerve guided by ultrasound at this level
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The endpoint of injection is complete perineural spread of local anaesthetic
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– Locate the pulsating popliteal artery at the level of the popliteal crease
– Look for the tibial nerve between the artery and the skin
– Look for the common peroneal nerve lateral to the tibial nerve
– Track the tibial nerve and the common peroneal nerve proximally until they unite and become the sciatic nerve
It is easy and requires only a small volume of local anaesthetic to anaesthetise the two branches of the sciatic nerve – the tibial nerve and the common peroneal nerve – individually
The two sciatic branches are easy to access as they are more superficially located than the sciatic nerve before the bifurcation
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